Capacitive touchpad is widely used as pointing devices in computer systems. Conventional capacitive touchpad detects the capacitance variance occurred in a sensor array, arranged in one-dimensional or two-dimensional manner, to determine the position of the finger touched thereon, and the movement and moving speed of the finger are determined by the variance of the position. The application for a mouse Z-axis are shown in FIGS. 1A and 1B. On a capacitive touchpad 10 there is a plurality of sensors 12 each coupled to a corresponding one of traces X1-X8 in a row of scan lines 16 coupled to a controller 14. When a finger touches the capacitive touchpad 10, the capacitance variance is detected by scanning the sensors 12, whose waveform is shown in FIG. 1B, to determine the position of the finger touched on the panel. For example, the distribution shown in FIG. 1B will determine that the finger touches on the sensor coupled to the trace X5, since the peak capacitance variance occurs at the trace X5. When the finger slides on the touchpad 10, the position that produces the peak capacitance variance moves as well, and therefore, the movement and moving speed of the finger may be determined by the moving peak capacitance variance to further produce a Z-axis signal.
However, when the number of the sensors 12 increases, the number of the corresponding traces increases as well, and the application circuitry within the controller 14 also becomes more complex, thereby increasing the chip size and the manufacture and package cost therefor.
Therefore, it is desired a capacitive touchpad with fewer traces and a method thereof to reduce the cost and to simplify the application circuitry and to easily achieve the design of mouse Z-axis.